Howard Markel and Alexandra Minna Stern are, respectively, the Director and the Associate Director of the Center for the History of Medicine at the University of Michigan. Both serve as historical consultants on pandemic preparedness planning for the Division of Global Migration and Quarantine, which is part of the U.S. Centers for Disease Control.

The first question to President Obama during Wednesday’s press conference was about whether he’d consider closing the border with Mexico. If you listen to cable television or check around the Internet, you’ll hear that same question--along with some nastier insinuations and conpsiracy theories about Mexicans and their government.

This is all very predictable. And counter-productive.

Epidemics always have scapegoats. In 1892, Eastern European Jews were blamed for outbreaks of typhus and cholera in New York City. In 1900, the Chinese were excoriated for a plague outbreak in San Francisco. Gays were singled out for for HIV/AIDs in the 1980s, Asians for SARS in 2003.

The scapegoating is even worse during economic downturns. And this isn’t the first time that’s made it tough on Mexican-Americans--the majority of whom, documented and undocumented, have come to this country seeking jobs at times of labor market distress. During the Great Depression, up to 30 percent of the Mexican-origin population in the United States was forcibly repatriated.

The U.S. isn’t the only country that reacts to epidemics this way. Russia has banned all Mexican pork products from its grocery stores, despite definitive evidence that humans do not contract swine flu from eating pork. In Israel, the health officials re-named the disease "Mexican flu.”

As it happens, Mexico itself has a history of blaming foreigners for epidemics. During the early 20th century, Mexicans focused blame for disease outbreaks on the Chinese, whom they called a pestilent race. This Sinophobic fever peaked in 1930 with the mass expulsion of Chinese residents from the northern state of Sonora.

Seven decades later, some of those same sentiments remain. Just days ago, the governor of Vera Cruz denied that swine flu had come from his state, declaring that the virus actually originated from “Asia, in China; it came from there, from American visitors and surely from Mexico City and the state of Mexico. It is not associated with the pork industry in the Perote Valley.”

Not only is such behavior a reflexive exercise in racism. It is, quite simply, a huge detriment to the public health. When groups start getting blamed for epidemics, members of those groups will start to fear--sometimes legitimately--that they will be stigmatized, mistreated, or punished if they seek medical attention. So they simply don’t go to the doctor or hospital, at least not until it’s too late for treatment and too late for detection to have done the most good. Taking care of these people, and containing the outbreak, becomes a great deal harder.

This isn’t mere conjecture. It’s been documented in numerous public health studies. And we’re already seeing anecdotal evidence of this phenomenon. There are stories of mistreatment--real or not--circulating in the immigrant press. According to the Associated Press, some Mexican-Americans in California say that medical professionals are turning them away.

In the coming weeks, we have a lot of work to do--and little time for this sort of scapegoating. Blaming the victim of an epidemic is akin to using lancets for bloodletting: sharp, painful, and counter-productive. And, like bloodletting, it should belongs in a museum--as a historical relic.

--Howard Markel and Alexandra Minna Stern